Certain vehicle designs selectively utilize multiple energy sources in order to improve overall fuel economy, as well as to reduce levels of certain vehicle emissions. For example, a hybrid electric vehicle or HEV includes a rechargeable energy storage system (ESS) which is usually configured as a rechargeable battery or battery pack having a relatively high energy density. The HEV can also include a gasoline, diesel, or alternative fuel internal combustion engine. Other vehicle designs may alternately employ a fuel cell and/or another power source in place of or in conjunction with an internal combustion engine in order to further reduce vehicle emissions and improve the operating range of the vehicle.
In certain HEV designs, the drive wheels of the vehicle remain continuously connected to the driveline to enable regenerative braking capability, thus providing a relatively efficient means of capturing useful and otherwise wasted braking energy. As is known in the art, an electric motor/generator can be selectively operated in such a manner as to allow the device to act as a generator during an active regenerative braking event. When acting as a generator, the electric motor/generator recharges the ESS while applying a negative torque to the drive wheels and/or the drive shaft, thus electronically slowing the HEV. The electric motor/generator likewise can be selectively operated as an electric motor, thus drawing stored electrical energy from the ESS as needed to propel the HEV.
In an HEV equipped with antilock braking system (ABS), a traction control system (TCS), and/or electronic stability control (ESC), vehicle stability and steering performance can be improved using any or all of these devices. During an active regenerative braking event in an HEV, however, regenerative braking torque is ordinarily applied only to the wheels rotating on a common axle, which can potentially slip on a low coefficient of friction surface. Depending on which of the front or rear sets of wheels are slipping, the overall stability and/or steering control of the HEV can be affected. While ABS, TCS, and ESC each can help the HEV to quickly recover from such slip, it may be more desirable to prevent or preempt slip from occurring in the first place.